Diamond Lake IA 03-NSK-861

Poweshiek County S2T78NR15W approx 2.5 mi SW of Montezuma.

Open Data Collection Period Modal

For purposes of developing stream/river water quality assessments for integrated reporting, three years of water quality data are typically used for both conventional pollutant parameters (e.g., indicator bacteria) and the less frequently monitored toxic parameters (e.g., toxic metals). Since the 2004 IR cycle, DNR has used a three-year data gathering period for streams, rivers, and beaches. For most assessments, the use of three years of data increases the number of samples upon which the decision on use support is based and helps address the problem of weather-related year-to-year fluctuations in water quality.

Due to the lower sampling frequency in Iowa’s ambient lake, biological, fish kill, and fish tissue monitoring programs, five years of data are used for developing IR assessments and for identifying Section 303(d) listings.

Data Type	Data Timeframe
Beach Sampling Data	CY 2018 - 2020
Stream/River Water Quality Data	CY 2018 - 2020
Lake Water Quality Data	CY 2016 - 2020
Biological Sampling Data	CY 2016 - 2020*
Fish Kill Data	CY 2016 - 2020
Fish Tissue Sampling Data	CY 2016 - 2020
Continuous Dissolved Oxygen Sampling Data	CY 2016 - 2020
*Biological sites sampled in both 2015 and 2019 were also assessed.

Open Segment Map
View assessment methodology in new window

Cycle: 2022
Release Status: Final
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trophic: Eutrophic
Trend: Stable
Created: 12/22/2021 1:34:24 PM
Updated: 7/6/2022 12:46:15 PM

Use Support

Class BLW

Aquatic Life - Lakes and wetlands

Not Supported

Exotic/Invasive Species: Fish Species

Support Level

Further Investigation Needed

Impairment Code

3b - Use potentially impaired based on an evaluated assessment.

Cause Magnitude

Slight

Status

Continuing

Source

Other: Exotic Species

Source Confidence

Moderate

Cycle Added

2016

Impairment Rationale

Adverse impacts on plant/animal communities

Data Source

Biological monitoring: Iowa DNR Fisheries

Algal Growth: Chlorophyll a

Support Level

Not Supported

Impairment Code

5* - 303(d)-impaired last cycle; fully supporting this cycle; potential de-listing.

Cause Magnitude

Moderate

Status

Continuing

Source

Agriculture

Source Confidence

Moderate

Cycle Added

2020

Impairment Rationale

Adverse impacts on plant/animal communities

Data Source

Ambient monitoring: Iowa DNR-shallow lakes & wetlands

TMDL Priority

Tier I

Class C

Drinking Water -

Fully Supported

Class HH

Human Health -

Fully Supported

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class BLW use was assessed as “WINOFI” due to poor water quality caused by an exotic fish population (common carp). High levels of algae at this wetland also suggested impairment due to aesthetically objectionable conditions. The Class C use was assessed as “fully supported” based on water quality monitoring data. The Class HH (fish consumption) use was assessed as "fully supported" based on fish tissue sampling data.

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2016-2020	22790005	Diamond Lake
Iowa DNR	6	FT	See Below	294	Diamond Lake

Class BLW - TSI's

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Minimum Value	Maximum Value	Median Value	Median TSI Violation?	Assessment Type	Support Level
22790005	6	Chlorophyll a TSI	15 / 5	35	80	63	NO	Monitored	Full
22790005	6	Inorganic suspended solids	15 / 5	2.4	22	8	NA	NA	NA

Although the index value for Chlorophyll a is below the impairment trigger of 65 for this assessment cycle, the Class BLW use of Diamond Lake remains "not supported" due to aesthetically objectionable conditions. Based on DNR's methodology, the median TSI value for Chlorophyll a must be 63 or less for two consecutive assessment/listing cycles before a river can be removed from the state's Section 303(d) list (IR Category 5). Therefore, Diamond Lake will remain listed as "not supported" for the 2022 assessment/listing cycle.

Class BLW - Conventional Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Minimum Value	Maximum Value	Mean Value	# Violations	# Acute / Chronic Violations	Violations needed for impairment	Violates Significantly >10% Rule?	Assessment Type	Support Level
22790005	6	Ammonia	15 / 5	0.0003	0.488	0.14	NA	0 / 0	4	NO	Monitored	Full
22790005	6	Dissolved Oxygen	15 / 5	3.5	13.4	8.6	1	NA / NA	4	NO	Monitored	Full
22790005	6	pH	15 / 5	7.2	8.8	8.2	0	NA / NA	4	NO	Monitored	Full
22790005	6	Temperature	15 / 5	19.1	28.8	24	0	NA / NA	4	NO	Monitored	Full

Class BLW - Lake Planktonic Cyanobacteria:

Site ID	Data Source ID	# Samples	Maximum Cyanobacteria Wet Mass	Maximum Cyanobacteria % Composition	Median Cyanobacteria Wet Mass	Median Cyanobacteria % Composition	Median Cyanobacteria Concentration = 75th Percentile	Assessment Type	Support Level
22790005	6	6	26.00	90.5%	7.91	54.1%	NO	Evaluated	NA

Class C - Conventional Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Minimum Value	Maximum Value	Mean Value	Median Value	# Violations	Violates Significantly >10% Rule?	Assessment Type	Support Level
22790005	6	Inorganic nitrogen (nitrate and nitrite)	15 / 5	0.02	2.2	0.4	0.035	0	NO	Mon	FS
22790005	6	pH	15 / 5	7.2	8.8	8.2	8.3	0	NO	Mon	FS

Class HH - Fish Tissue Sampling:

Site ID	Biopart	Year	Species	# in sample / # of samples	Avg Length (cm)	(Avg) Hg (ppm)	Chlordane (ppm)	Sum PCBs (ppm)
294	fillet	2013	channel catfish	5	43	0.05	<0.2	<0.6
294	tissue plug	2013	largemouth bass	5	35.6	0.124
Support Level	Full

Monitoring and Methods

Assessment Key Dates

6/22/2016

Non-fixed Monitoring Start Date

9/16/2020

Non-fixed Monitoring End Date

7/31/2013

Fish Tissue Monitoring

Methods

120

Surveys of fish and game biologists/other professionals

222

Non-fixed-station monitoring (conventional during key seasons and flows)

260

Fish tissue analysis

270

PWS chemical monitoring (ambient water)

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)